Historic Camera Collector Club
|DICTIONARY OF PHOTOGRAPHY
by E.J. Wall
Single lenses were first of all of the kind shown in fig. 4, with which extremely small diaphragms are necessary to reduce
spherical aberration and distortion. This was improved on by Grubb, and his lens is shown in fig. 10, in which a crown-glass lens of meniscus form is presented to the object, and is cemented to a flint meniscus. This gave a much flatter field, and spherical aberration was much reduced, allowing the use of larger diaphragms.
Dallmeyer introduced his single lens (fig. 11), which consists of a negative flint enclosed between two positive crown-glass lenses. This enabled a much larger aperture to be employed,
and totally eliminated spherical aberration. Marginal definition and flatness of field were both improved.
To obviate distortion, many doublet lenses were introduced, that of Mr. Ross being shown in fig. 12. This instrument possesses a wide angle, giving splendid definition, without any distortion or aberration.
In all doublets, the diaphragm being placed between the combinations,
the distortion of the one is cured by the distortion of the other. In 1860 Harrison, of New York, introduced his globe lens (fig. 13), which had an extremely wide angle, but which, from too close an adherence to the globe form, gave a flare.